T12 florescent tubes are more energy efficient than incandescent (regular bulbs)
T8 more efficient than T12
T5 more efficient than T8
T12s are being phased out in the USA.
certain T8s will be phased starting in July in the USA.
6500K is the best temperature for plants. If you can't find them, get the closest you can find, most likely a lower temperature K.
The lower you go, the less light usable by plants is produced.
High output 4ft T5 6500K (54W) is what I am transitioning to.
4ft models are slightly more energy efficient than twice as many of the 2ft models.
It might be a concern that the heat from the ballasts and lights will be too much in an insulated box. (or it may be a benefit.) You will have to monitor the temps.
I am not sure if Lorn's "12-15 inches above the plant" is actually above the plant or above the table that the pot and plant sits on. 12-15" above the plant itself seems to me to be quite a long way. Lumens lost per inch of distance is hugely substantial with florescent tubes. When I used cool white T12s, my tomatoes and peppers would grow up into the light fixture and sometimes leaves actually touched the tubes. They loved it. With 6500K, I would aim for the closest plant leaves to be at about 4 inches away, if possible. In a more practical sense, you probably be farther. LED technology for plants hasn't advanced enough yet to use for plants, IMO.
